The present invention relates to a transistor and a semiconductor device, more particularly to a transparent transistor, a semiconductor device having the transparent transistor stacked thereon, and a semiconductor device to which the transparent transistor is applied for driving a light emission device, for reading/writing data from/to a memory, and for other purposes. It should be noted that in the present invention, a concept of xe2x80x9ctransparentxe2x80x9d includes a concept of xe2x80x9cbeing transparent or offering light transmission propertyxe2x80x9d for the sake of simplifying descriptions.
A thin film transistor using amorphous silicon, polycrystalline silicon or the like has been generally used as a transistor for use in driving liquid crystal display devices. Since these materials exhibit photosensitivity for the visible light region, carriers are generated by a beam of light, and resistivity of a thin film constituting the thin film transistor is lowered. For this reason, when the beam of light is radiated thereonto, the transistor may be made to be a turn-on state, in spite of the fact that the transistor must be controlled to be a turn-off state. Accordingly, to keep the transistor at the turn-off state, the lowering of the carrier resistivity of the thin film due to the radiation of the beam of light has been heretofore prevented by the use of a light shielding layer made of a metal film or the like.
Generally, the liquid crystal display device has been widely used for a notebook type personal computer or the like, and an energy-saving measure, a high luminance and a miniaturization have been requested of the liquid crystal display device. To reply to these requests, it is effective to increase a rate of an effective area of a display portion within a unit pixel. However, since a light shielding layer made of a metal thin film or the like in the transistor for driving the liquid crystal display device is formed as described above, a rate of an area of a light transmission portion to that of the light shielding layer (opening ratio) in the pixel reduces. Accordingly, a reduction of a transistor area by improving a performance of the transistor or an improvement of luminance of a backlight are necessary to develop a display device having high luminance. However, the measure to improve the characteristic of the transistor shows a limitation to a yield, leading to an increase in cost. Moreover, the measure to improve the luminance of the backlight increases an amount of energy consumption.
From the viewpoint of the above described points, the object of the present invention is to provide a transistor using a transparent channel layer made of zinc oxide or the like, which is transparent partially or entirely, because an orientation control of the zinc oxide and a valence electron control thereof that has been heretofore difficult is now possible. Specifically, the object of the present invention is to provide a transistor which uses a transparent material such as the zinc oxide or the like for a channel layer (conductive layer) so that the channel layer does not have a photosensitivity for the visible light region, and removes a necessity to form a light shielding layer, thus increasing an area rate of a display portion of a liquid crystal display device or the like.
Furthermore, the object of the present invention is to use a transparent transistor for various kinds of applications in an optical device field for use in driving a light emission device such as a plane light emission laser and an electroluminescence device and for use in a memory. Still furthermore, the object of the present invention is to provide a semiconductor device used as a transparent electronic device for various kinds of wide applications in addition to a driving circuit requiring no light shielding layer.
According to first solving means of the present invention, a transistor is provided,
which comprises:
a transparent channel layer using any one of zinc oxide ZnO, zinc magnesium oxide MgxZn1xe2x88x92xO, zinc cadmium oxide CdxZn1xe2x88x92xO and cadmium oxide CdO; and
a source, a drain and a gate in which a transparent conductive material such as conductive ZnO doped or undoped with any one of group III elements, group VII elements, group I elements and group V elements, a transparent conductive material such as In2O3, SnO2 and (Inxe2x80x94Sn)Ox, or an untransparent electrode material are used partially or entirely.
According to second solving means of the present invention, a transistor is provided,
which comprises:
an emitter and a collector, or a base which are made of a transparent n-type semiconductor such as ZnO doped with group III elements or group VII elements;
a base, or an emitter and a collector which are made of a transparent p-type semiconductor such as ZnO doped with group I element or group V elements; and
a base electrode, an emitter electrode and a collector electrode respectively formed on the base, the emitter and the collector, in which a transparent conductive material such as conductive ZnO doped or undoped with any one of group III elements, group VII elements, group I elements and group V elements, a transparent conductive material such as InO3, SnO2 and (Inxe2x80x94Sn)Ox, or an untransparent electrode material are used partially or entirely.
Still another object of the present invention is to provide a semiconductor device in which a transparent transistor is stacked, and a semiconductor device applied to a light emission device, a memory or the like.